Preparation of a liquid fuel for a pressure-type atomizer

ABSTRACT

DECREASING THE VISCOSITY OF AND IMPROVING THE ATOMIZING AND BURNING CHARACTERISTICS OF A HEAVY HYDROCARBON BY DISSOLVING A NON-HYDROCARBON GAS IN THE HEAVY HYDROCARBON IN AN AMOUNT NOT EXCEEDING 95% OF SATURATION AT CONDITIONS OF TEMPERATURE AND PRESSURE IMMEDIATELY PRECEDING ATOMIZATION

United States Patent 3,672,853 PREPARATION OF A LIQUID FUEL FOR A PRESSURE-TY PE ATOMIZER Gerrit H. Reman and Henri Verkoren, Amsterdam, Netherlands, assignors to Shell Oil Company, New York, N.Y.

No Drawing. Filed Apr. 21, 1969, Ser. No. 818,074 Claims priority, application Netherlands, Apr. 22, 1968, 6818913 Int. Cl. C101 1/00 US. Cl. 44--52 5 Claims ABSTRACT OF THE DISCLOSURE Decreasing the viscosity of and improving the atomizing and burning characteristics of a heavy hydrocarbon by dissolving a non-hydrocarbon gas in the heavy hydrocarbon in an amount not exceeding 95% of saturation at conditions of temperature and pressure immediately preceding atomization.

BACKGROUND OF THE INVENTION The invention relates to a process for the preparation of a liquid fuel suitable to be handled in a pressure-type atomizer, using a hydrocarbon-containing feed as base material.

A hydrocarbon-containing feed may consist of hydrocarbons. It is also possible for such a feed to consist of hydrocarbons to which are added asphaltenes, soot particles, coke particles or coal particles or combinations thereof. The hydrocarbons may consist entirely or substantially of distilled fractions and may also consist entirely or substantially of residual fractions. Furthermore it is possible to use a crude oil as such.

Handling fuel in a pressure-type atomizer is a procedure which is widely employed in practice. The fuel is passed under high pressure-for instance up to 150 kg./cm. to an atomizer, which results in the formation of minute droplets of liquid which leave the atomizer to enter a combustion chamber. The temperature of the feed in the atomizer is chosen to be so high that the viscosity of the feed is low enough for the feed to be atomized. One aims at a viscosity below 100 cs., preferably below 20 cs.

An increase in temperature as a means to reach a sufficiently low viscosity as referred to hereinbefore is subject to limitations. Generally as upper limit is taken the temperature at which thermal decomposition of one or more components of the feed may occur. For many feeds this temperature lies at approximately 350 C. For this reason heavy feeds, which then do not meet the requirements as regards viscosity, cannot be handled. This is a great disadvantage, because such heavy feeds are often comparatively cheap or are composed partly of by-products such as soot or asphaltenes. The invention provides a process by which this disadvantage is to a considerable extent obviated.

The invention therefore relates to a process for the preparation of a liquid fuel suitable to be handled in a pressure-type atomizer, using a hydrocarbon-containing feed as base material, in which process a gas not belonging to the hydrocarbons is dissolved in the feed in an amount not exceeding 95% of the maximum amount that can dissolve at the temperature and the pressure prevailing in the line immediately before the pressure-type atomizer.

Owing to this measure remarkably high reductions in viscosity are reached. It has been found that the viscosity of a base material whose viscosity is very high can be reduced to a value-measured at the same temperaturebeing one third of the original value. This means, in addiice tion, that with a fuel prepared according to the invention it is possible to attain a reduction by 40 C. of the minimum temperature required to enable the fuel to be handled in a pressure-type atomizer as compared with the minimum temperature which the feed used as base material requires for this purpose.

Furthermore it has been found that the dissolved gas has a favorable effect on the atomization of the fuel. As a result of the pressure in the pressure-type atomizer decreasing very rapidly, the solubility of the gas also decreases. Gas thus being liberated contributes to the liquid droplets being split up to a larger extent. In this connection it is of great importance that no formation of gas bubbles takes place in the pressure-type atomizer. Otherwise the flame generated would be irregular owing to repeated short interruptions of the fuel flow from the atomizer. This phenomenon may even cause the flame to be extinguished. In consequence of the decrease in the pressure in the pressure-type atomizer the fuel reaches a condition where the solution cannot be stable any longer. The gas starts to leave the solution. However, the residence time of the fuel in the zone where the pressure decreases in the pressure-type atomizer is very short. During that short time the process of gas leaving the solution just gets going. Now, by reducing the amount to be dissolved in the feed to not more than of the maximum amount that can dissolve at the temperature and the pressure prevailing in the line immediately before the pressure-type atomizer the formation of gas bubbles in the pressure-type atomizer is prevented, so that the stability of the flame is maintained. Also, it is ensured in this way that the dissolved gas entirely serves the purpose of improving the atomization.

The maximum amount of gas that can dissolvebesides being dependent on the temperature and on the pressure-is determined by the nature of the gas and of the feed. This amount can be assessed experimentally. It will then be possible for the desired amount of gas to be dissolved to be added in proportion to the feed flow.

According to another characteristic of the invention the gas is dissolved at a lower temperature and/or a lower pressure than the temperature and pressure prevailing in the line immediately before the pressure-type atomizer, whereupon the fuel, before being passed to the atomizer, is brought to a temperature and a pressure as prevailing in the line immediately before the pressure-type atomizer, such gas as is possibly liberated being removed before a final pressure stage. In this way it will always be possible to add the amount of gas to be dissolved accurately in proportion to the feed flow, for the solubility of the gas generally decreases with increasing temperature and increases with increasing gas pressure. By selecting the conditions at which the gas is dissolved in such a way that a suitable combination is attained it will always be possible to attain the desired amount at the conditons prevailing immediaely before the atomizer. Such gas as is possibly liberated may be drawn off at a pressure that is just a little lower than that prevailing immediately before the pressure-type atomizer. Then, when the liquid pressure is further increased, the solution is no longer saturated.

It is also possible for the feed to be saturated with gas at a pressure which is slightly lower than the pressure prevailing in the line immediately before the pressuretype atomizer and at a temperature which is equal to the temperature in that line. When the liquid pressure is further increased the solution at the new conditions becomes unsaturated.

Very favorable eifects are obtained if the gas consists of water vapor. Favorable effects are also attained with carbon dioxide or with hydrogen, as appears from the examples to be discussed hereinafter. It is likewise possible to use combinations of gases. The dissolution of water vapor or carbon dioxide not only yields the aforementioned effects of a decrease in viscosity and improvement of the atomization but also decreases the formation of soot during the combustion.

In the case of water vapor being used, water in the form of minute droplets can be introduced into the feed under pressure, at a lower temperature than that prevailing in the line immediately before the pressure-type atomizer, which water, owing to the temperature subsequently being increased, vaporizes and dissolves in the feed, such water vapor as has not dissolved being removed before the fuel is passed to the atomizer. This procedure offers great advantages from a technical point of view, since water is cheap and permits of easy dosage. The process conditions should -be chosen in such a way that the water present in the fuel immediately before the pressure-type atomizer is dissolved therein in such an amount that the solution is saturated to an extent of at most 95%. If droplets of water should still be present there, then the intended decrease in viscosity would not be reached.

If it is possible for the temperature and the pressure to be chosen so that the critical point for the gas in question is exceeded, then the risk of liquid being formed from that gas is no longer present. For water the critical point lies at 374 C. and 218 kg./cm. These values are high, but can nevertheless be reached in practice.

The advantages of the process according to the invention are apparent particularly in combustion processes using very heavy fuels. Likewise of great importance is the application to a process for the preparation of gases containing carbon monoxide and hydrogen by partial combustion ofa hydrocarbon-containing feed with an oxygen-containing gas in a reactor at a pressure higher than 1 kg./ cm). In a process of this type the formation of soot is diflicult to prevent. Usually the soot is removed from the stream of product gas by washing with a liquid, for instance with Water. Removal of the soot from the soot slurry obtained can be achieved, for instance, by agglomeration with a hydrocarbon. Such agglomerates can again be introduced into the feed as finely divided particles, so that a fuel is obtained which likewise contains carbon in the form of minute particles. This, however, results in a considerable increase in the viscosity. The process according to the invention enables an important decrease in the viscosity to be attained, as a result of which the amount of soot that can be introduced into a certain feed is increased until the upper limit of the range of viscosities that are permissible in the atomization is reached again.

EXAMPLE I Viscosity in cp.

Feed with dis- Temperature, C. Feed solved CO2 Thus, by dissolving carbon dioxide the viscosity of this very heavy feed is reduced by approximately a factor of EXAMPLE II A sample of a similar feed to that used in Example I was brought to a hydrogen pressure of 220 kg./cm. Herewith, in similar measurements to those described in Example I the following results were reached:

Viscosity in cp.

Feed with dis- Temperature, 0. Feed solved H2 In this case also straight lines as described herebefore are obtained. It follows from this that a viscosity of 100 cp. is reached for the feed at 358 C. and for the feed with dissolved H at 321 C. This is a very considerable reduction.

EXAMPLE HI A sample of the same feed as that used in Example I was brought to a steam pressure of 60 kg./cm. Herewith, in similar measurements to those described hereinbefore the following results were obtained:

Viscosity in cp.

Feed with dis- Temperature, 0. Feed solved H20 In this case also straight lines as described hereinbefore are obtained. It follows from this that a viscosity of 100 cp. is reached for the feed at 350 C. and for the feed with dissolved H O at 316 C. This is a very considerable reduction.

It should be noted that the viscosities mentioned in the examples are expressed in cp. As the densities of the liquids measured will differ little from 1, the values of the viscosity expressed in cs. will differ little from those in cp.

What we claim is:

1. A process for the preparation of a liquid hydrocarbon-containing fuel from a heavy hydrocarbon-containing feed, whereby the fuel is suitable to be handled in a pressure-type atomizer comprising dissolving a gas selected from the group consisting of carbon dioxide hydrogen and water vapor in the feed in an amount not exceeding of the maximum amount that can dissolve at the temperature and the pressure prevailing in the line immediately before the pressure-type atomizer.

2. A process according to claim 1, wherein the gas is dissolved in the feed at a lower pressure than the pressure prevailing in the line immediately before the pressure-type atomizer.

3. A process according to claim 1, wherein the gas consists of water vapor.

4. A process according to claim 1 wherein the gas consists of carbon dioxide.

5. A process according to claim 3 wherein water in the form of minute droplets is introduced into the feed under pressure and at a lower temperature than that prevailing in the line immediately before the pressure-type atomizer, subsequently increasing the temperature and removing excess water vapor before the fuel is passed to the atomizer.

References Cited UNITED STATES PATENTS 890,620 6/ 1908 Diesel 4452 6 Gronkwist 48219 Gaertner 44-52 X Schlumbohm 4452 X De Lamprecht 44-52 X Strouse 44-52 X Donnelly 48-213 X DANIEL E. WYMAN, Primary Examiner 1,519,830 12/1924 Goeriz 48214 10 W. J. SHINE, Assistant Examiner 

